In a food processor or blender, add tomatoes, reserved 1/2 cup liquid and chipotles - process until almost smooth.

In a large skillet, add oil and heat over medium high. Stir in about two-thirds of the onion - cook until browned around the edges, about 6 minutes. Stir in the garlic and cook until fragrant, about 1 minute. Pour in the tomato puree - simmer, stirring often, until slightly thickened, about 5 minutes. Stir in the stock - bring to a boil and cook until slightly thickened, about 2 minutes. Season to taste with salt and remove from the heat.

Add the tortilla chips to the sauce and gently stir to coat them well. Top with the remaining onion, the shredded chicken and the Asiago cheese. Evenly dollop the sour cream over the chilaquiles and sprinkle with cilantro to serve.